#include <bits/stdc++.h>

using namespace std;

// A Dequeue (Double ended queue) based method for printing maximum element of
// all subarrays of size k

ifstream fin("deque.in");
ofstream fout("deque.out");

int suma = 0;

void printKMax(int arr[], int n, int k)
{
	// Create a Double Ended Queue, Qi that will store indexes of array elements
	// The queue will store indexes of useful elements in every window and it will
	// maintain decreasing order of values from front to rear in Qi, i.e.,
	// arr[Qi.front[]] to arr[Qi.rear()] are sorted in decreasing order
	std::deque<int> Qi(k);

	/* Process first k (or first window) elements of array */
	int i;
	for (i = 0; i < k; ++i) {
		// For every element, the previous smaller elements are useless so
		// remove them from Qi
		while ((!Qi.empty()) && arr[i] <= arr[Qi.back()])
			Qi.pop_back(); // Remove from rear

		// Add new element at rear of queue
		Qi.push_back(i);
	}

	// Process rest of the elements, i.e., from arr[k] to arr[n-1]
	for (; i < n; ++i) {
		// The element at the front of the queue is the largest element of
		// previous window, so print it
		//cout << arr[Qi.front()] << " ";
		suma += arr[Qi.front()];

		// Remove the elements which are out of this window
		while ((!Qi.empty()) && Qi.front() <= i - k)
			Qi.pop_front(); // Remove from front of queue

		// Remove all elements smaller than the currently
		// being added element (remove useless elements)
		while ((!Qi.empty()) && arr[i] <= arr[Qi.back()])
			Qi.pop_back();

		// Add current element at the rear of Qi
		Qi.push_back(i);
	}

	// Print the maximum element of last window
//	cout << arr[Qi.front()];
	suma += arr[Qi.front()];
	fout << suma;
}

// Driver program to test above functions
int main()
{
    int p;
    fin >> p;
	int arr[p];
	int k;
	fin >> k;
	for(int i = 0; i < p; ++i) {
        fin >> arr[i];
	}
	int n = sizeof(arr) / sizeof(arr[0]);
	printKMax(arr, n, k);
	return 0;
}